This content shows how to better understand SAR (how to interpret SAR images and read SAR interferogram ). Moreover, capacities and limitations of SAR are discussed for each disaster emergency mapping (Flood, Landslide and Earthquake).
How to better understand SAR, interpret SAR products and realize the limitations
1. Graduate School of Sciences and Technology of Innovation
Yamaguchi University, Japan
Nopphawan Tamkuan and Masahiko Nagai
How to better understand SAR, interpret
SAR products and realize the limitations
7. Real Aperture Radar (RAR) Synthetic Aperture Radar (SAR)
Synthetic Aperture Radar (SAR) is side
looking radar which utilizes fight path to
increase the antenna’s size (aperture)
and resolution in azimuth direction.
This system uses complicated data
processing of multi-temporal signals
and phase receiving from targets to
generate high resolution image.
26. Limitations of SAR utilization for damage mapping
One SAR during flood
(Thresholding)
Discussions
• Include permanent water and flat land
• More difficult for flood under vegetation
and urban areas.
• Image change to be discrete value
Flood
27. Limitations of SAR utilization for damage mapping
Two image method
(Thresholding)
Discussions
• Better than just one image
• differentiate waterbody and seasonal water
from flood
• Seasonal difference 🡪 difficult to compare
• Better to use 2 image near time or in the
same season
Flood
28. Limitations of SAR utilization for damage mapping
Two image method
(Color composite)
Discussions
• More gradience value 🡪 more
information
• More difficult for interpretation
• Same SAR limitations
• Should consider seasonal effect
of different time acquisition to
interpretation
Flood
29. Before flood
During flood During flood
red color
Flood is
During flood
During flood Before flood
dark blue
Flood is
30. Limitations of SAR utilization for damage mapping
Two image method (needed)
Discussions
• Same SAR limitations
• More effect for geometry distortion
Landslide
33. Limitations of SAR utilization for damage mapping
Differential SAR Interferometry
(DInSAR)
Discussions
• Fringes 🡪 Difficult to understand
• Just relative displacement
• Interferogram has many
components. Not only surface
deformation but also other effects
such as atmospheric delay,
topographic phase and noise.
Earthquake
38. Close to
sensor
Far away
from sensor
Close to sensor
Far away from sensor
N
2D
Flight direction
Look direction
Kumamoto Earthquake
In 2016
39. Close to
sensor
Far away
from sensor
N
2D
Flight direction
Look direction
High
Low
Close to sensor
Far away from sensor
40. Close to
sensor
Far away
from sensor
N
2D
Flight direction
Look direction
Fujiwara, S., Yarai, H., Kobayashi, T., Morishita, Y., Nakano, T., Miyahara, B., … Une, H. (2016). Small-displacement linear surface ruptures of the 2016
Kumamoto earthquake sequence detected by ALOS-2 SAR interferometry. Earth, Planets and Space, 68(1), 160. https://doi.org/10.1186/s40623-016-0534-x
41. Limitations of SAR utilization for damage mapping
Interferometric coherence
change
Discussions
• Need 2 image before and one after
earthquake
• Show damage possibility
• Many decorrelation effects
• Noise in the radar system and processing
approach
• geometric coherence proportional to the
perpendicular component of the baseline
• influence of temporal backscatter change, e.g.
from surface cover change or vegetation
• No identify individual building but
show as grid result
Earthquake
44. Conclusion
SAR plays important role in disaster response phase because it
can observe night and daytime, penetrate cloud and less
atmospheric effects.
However, SAR is different from optical sensor and difficult to
understand.
It is better to realize SAR characteristics and limitations to better
understand disaster mapping.
